1. Field of the Invention
The present invention relates to a method of manufacturing a fine-patternable carbon nano-tube (CNT) emitter for a field emission device (FED) with high reliability, and more particularly, to a method of manufacturing a CNT emitter which employs a CNT paste including a nano-sized metal particle, an organic binder, a photosensitive material and a monomer, and a fine-patterning process to manufacture the CNT emitter.
2. Discussion of Related Art
A physical function of a field emission device (FED) is principally the same as that of a cathode ray tube (CRT) except for an electron emission source of the CRT that is formed of a cold cathode material. In the FED, an electric field is applied to a field emitter having an ultra-fine structure and an electron emitted into vacuum hits a fluorescent medium (i.e., exciting the fluorescent medium) so that an image is displayed. Therefore, the FED is a display device that has excellent display characteristics of the CRT, and can be lightweight and thin. Also, since the FED has ideal characteristics of a display device in all aspects, it has come into the spotlight as a promising next generation flat panel display.
A material that has recently gained attention as an electron emission source (emitter) of the FED is a carbon nano tube (CNT). The CNT is an emitter that applies the principle of field emission, in which an electron is emitted when an electric field is applied to a conductive emitter having a sharp end in a vacuum state, and provides excellent performance.
FIG. 1 is a side cross-sectional view of a conventional FED including a CNT emitter. FIG. 2 is an enlarged cross-sectional view of region II of FIG. 1.
Referring to FIG. 1, an FED 100 includes an electron emitter 110 in which an electron emission source is formed as an emitter 114, and an image generating part 130 including fluorescent layers 135 in which an electron emitted from the electron emitter 110 is hit to thereby generate light.
The image generating part 130 includes a second substrate 131, a positive electrode 133 (anode) formed on the second substrate 131, the fluorescent layers 135 formed spaced apart from each other on the positive electrode 133, and a light-shielding layer (black-matrix) 137 formed between the fluorescent layers 135. The light-shielding layer 137 is in charge of defining pixel boundaries.
The electron emitter 110 includes a first substrate 111, negative electrodes (cathodes) 113 formed spaced apart from each other on the first substrate 111 in a predetermined shape, a CNT emitter 114 formed on the negative electrode 113 using a CNT, and a gate electrode 119 that is insulated from the negative electrode 113. An insulating layer 118 is formed below the gate electrode 119. A spacer 140 supporting the electron emitter 110 and the image generating part 130 is formed between the electron emitter 110 and the image generating part 130.
To manufacture the CNT emitter 114 that constitutes the electron emitter 110, a CNT paste should first be manufactured. The CNT paste is manufactured by: (1) dispersing the CNT and an inorganic filler; (2) adding an organic binder; and (3) mixing the addition using a solvent and adjusting viscosity. Referring to FIG. 2, after the CNT paste is manufactured through processes (1) to (3), the CNT paste is coated on the negative electrode 113 of the electron emitter 110 to thereby form the CNT emitter 114.
However, when the CNT emitter 114 is manufactured using the above-described CNT paste, the conventional CNT paste employs a frit glass generally having a size of several μm as an inorganic (metal) filler 115. In this case, the frit glass has physically and chemically different characteristics from the CNT. Therefore, it is difficult to equally distribute the CNT that will be implemented as an emitter. Also, adhesion between the cathode 113 and the CNT 117 is not uniform. Furthermore, a resistance between the negative electrode 113 and the CNT 117 or one CNT 117 and another CNT 117 is considerably increased or is non-uniformly exhibited, and thus this presents an obstacle to the accomplishment of a function of the FED.
Since the CNT emitter 114 is formed above the negative electrode 113 without strong adhesion, when the CNT emitter 114 generates an intense electric field, the CNT emitter 114 may become detached from the negative electrode 113. As a result, a contact resistance between the CNT emitter 114 and the negative electrode 113 may be non-uniform or increased. Also, since only a part of the CNT emitter 114 contributes to the electron emission, beginning with deteriorated electron emission characteristics, a deteriorated electron emission site and non-uniform distribution of the electron emission appear. Furthermore, since only a part of the CNT emitter 114 is responsible for the electron emission, the life span of the CNT emitter 114 may be significantly reduced. Fine patterning that is required not only for the manufacturing of fine pixels suitable for high resolution but for improvement of the non-uniform electron emission is difficult to implement due to obstacles involved in a printing process.
To overcome these problems, other methods of manufacturing a CNT paste are disclosed in Korean Patent Application No. 2006-84912 (Applicant: Electronics and Telecommunications Research Institute). In the method, a nano-sized metal particle that can be melted at a low temperature where a CNT does not deteriorate is added so that adhesion through melted metal between a CNT emitter and a negative electrode can be improved, and a resistance between the electrode and the CNT and between respective CNTs can be reduced. At the same time, a uniform resistance is applied so that the electron is uniformly emitted and the density of an active emission site contributing to the electron emission is increased. As a result, a CNT that can obtain considerable reliability may be manufactured.
Based on the method, an improved CNT for an FED may be implemented. However, the manufacturing of the fine pixels suitable for the high resolution and implementation of the fine-patterning for forming a plurality of CNT emitter regions within a pixel require strengthened patterning characteristics by exposure of the paste. In a case of a photosensitive material required for the patterning by the exposure, a monomer that reacts thereto and an organic binder, when they do not completely burn-out after the plasticity, a work function for the electron emission in the CNT and out-gassing in vacuum are increased by an organic material remaining on a surface of the CNT. As a result, characteristics of the CNT emitter deteriorate.
However, when a plasticity temperature that is higher than a melting point of the nano-sized metal particle that is added into the CNT paste is applied for the sake of the burn-out of the organic material as above, a metal layer that is melted first at a low temperature and holds the CNT is damaged in the process of the burn-out of the organic material. As a result, a surface shape of the CNT emitter deteriorates, so that characteristics of the CNT emitter eventually deteriorate as well.